Difference Between Redshift and Doppler Effect

Doppler Effect and redshift are two phenomena observed in the field of wave mechanics. Both of these phenomena occur due to the relative motion between the source and the observer. The applications of these phenomena are enormous. Fields such as astronomy, astrophysics, physics, and engineering and even traffic control uses these phenomena. It is vital to have a proper understanding in redshift and Doppler Effect in order to excel in fields, which have heavy applications based on these phenomena. In this article, we are going to discuss Doppler Effect and Redshift, their applications, similarities between redshift and Doppler Effect, and finally the difference between Doppler Effect and redshift.

Doppler Effect

Doppler Effect is a wave related phenomenon. There are a few terms that needed to be defined in order to explain the Doppler Effect. Source is the place where the wave or the signal is originated. Observer is the place where the signal or the wave is received. The frame of reference is the non-moving frame with respect to the medium where the whole phenomenon is observed. The wave velocity is the velocity of the wave in the medium with respect to the source.

Case 1

The source is still with respect to the frame of reference, and the observer is moving with a relative velocity of V with respect to the source at the direction of the source. The wave velocity of the medium is C. In this case, the relative velocity of the wave is C+V. The wavelength of the wave is V/f0. By applying V = fλ to the system, we get f =(C+V) f0/ C. If the observer is moving away from the source, the relative wave velocity becomes C-V.

Case 2

The observer is still with respect to the medium, and the source is moving with a relative velocity of U in the direction of the observer. The source emits waves of frequency f0with respect to the source. The wave velocity of the medium is C. The relative wave velocity remains at C and the wavelength of the wave becomes f0 / C-U. By applying V = f λ to the system, we get f = C f0/ (C-U).

Case 3

Both the source and the observer are moving towards each other with velocities of U and V with respect to the medium. Using the calculations in Case 1 and Case 2, we get the observed frequency as f = (C+V) f0/ (C-U).

Redshift

Redshift is a wave related phenomena observed in electromagnetic waves. In the case where frequencies of certain spectral lines are known, the observed spectra can be compared to the standard spectra. In the cases of stellar objects, this is a very useful method to calculate the relative velocity of the object. Redshift is the phenomena of the shifting of spectral lines slightly to the red side of the electromagnetic spectrum. This is caused by sources moving away from the observer. The counterpart of the redshift is the blueshift which is caused by the source coming toward the observer. In redshift, the wavelength difference is used to measure the relative velocity.

What is the difference between Doppler Effect and Redshift?

• Doppler Effect is observable in all waves. Redshift is defined only to the electromagnetic spectrum.

• To apply; the Doppler effect can be used to calculate any one of the five variables in case the other four are known. Redshift is used only to calculate the relative velocity.